It is proposed to continue operating a facility for analytical, biomedical mass spectrometry. The major subdivisions of the resource will be (1) analytical service, (2) instrument development, and (3) method development. Electron ionization and chemical ionization techniques will be used for the analytical service and for collaborative research. Construction and testing of a fission fragment ionization mass spectrometer will be followed by its use for biomedical analyses. Methods will be developed for protein sequencing, nucleotide sequencing, and sensitive quantitative analyses.